Stabilization of xylidine



Patented Jan. 3, 1950 John C. Mun'day, .Cranford, -J., assignor 420 "Standard Oil Development "Company, a cor- :poration 'ofDlaware No Drawing. Application December 28, 1943, .-SerialiNo.515,970

lllils finvention relates i'to Ithe stabilization or aromatic amines against deterioration "by discoloration, eta, during storage.

.'Ai:omatlc amines -.'such .as .a'riiline, toluidine, xyli'dine, .t'c., are manually substantially colorless when 'fresiily prepared .or freshly distilled, but tend to darken in color during storage, the undesirableresiilts -;Joeing greatly accelerated by storageat elevated temper-a'tur.es.

ZIhe .iibject 'o'f lthemresen't .invention is .to stabilize isuchiaromaticanfines against discoloration .duringtstorage.

. Broadly, ,thelinvention comprises adding to the aromatic aniinesesmalhamount of .a stabilizer comprising essentially a ,pure thiocarbanilide .or alkyla'ted derivative thereof, and preparing such stabilizers from crude tor commercially available aromatic amines by reacting 'them with carbon disulfi'dep'and purifying the resultant pro'duct.

fiAlthough the amount of the stabilizer to be used may 'v-ary -=atioording to the in-tended duration -of storage and the-temperature ofstorage, as well as according to the particular"aronriatic amine and the particular stabilizer used, in general about .0l% to 3.0% of stabilizer will be sufficient, and usually about .05% to 0.5% by weight of stabilizer will be found most practical for giving satisfactory results.

Although the invention is intended to apply broadlyto the stabilization of any type of arom'atic aniines, "it believed particularly lappli cable to alkaryl amines, especially those having from 1 to 3 alkyl carbonatom's. The'invention' has been found "very .successfulfor the stabilization of xylidinaaeither'the .pure separateisomers or mixtures thereof. Other alkaryl amines whioh may be stabilized include the toluidines, :ortho, meta or,,para, or .mixtures thereof, the several ethyl anilines, cumidine (which is isopropylaniline), etc. "Dialky'la'ted and trialkyla'ted aryl amines areppr'eferre d. Although the invention is particularly applicable to such alkaryl amines, it may 'also'be 'usedlfor. stabilizing aniline, naphthylamines, and-the various derivatives of aniline in'which either orbo'th of thehy'drogens of the amino group are substituted by hydrocarbons, i. e.,'e ither alkyl'or aryl groups, e. g., inT'N-m'onomethyl aniline, N-dimethyl aniline, fN-monoethyl aniline, etc. "Thus .although the invention is particularly applicable to alkaryl primary amines, other amines such as secondary andt'ertiary amines may alsoibe' used.

The various .above described aromatic amines maybe stabilized alone ortogether with a diluent, such .as va hydrocarbon .solvent, e. .g., naphtha.

1'-Claim. Cl. 260-578) from only a few percent up to 10,20 or even 100 times the volume of .the aromatic :amines, as when added-togasoline -for use in internal combustion engines.

-In..car1 1ying.0ut.the invention, it is preferred to add .the stabilizer tothe aromatic amines as soon as the "latter hasbeen "prepared, or "immeclia'tely after distillation.

The "following experimental data will illustrate the tadvanta gescof Jthe invention:

EXAIVIPLE 1 A stabilizer was prepared by treating 2 parts by vol. of commercial xylidine"'(freshly redistilledmixture of isomeric xylidines) with 1 vol. of carbon disulfide at room temperature, allowing evolved hydrogen sulfide to escape over a period of several days. The resultant mixed tetramethyl --th-iocarbani-lides were then purified by adding several volumes .each of :ether and petroleum ether, todissolve unreacted :andgpartly reacted materials. .The.product,. awhite crystalline solid, was then filtered and dried-for use as stabilizer. After purification the productiis not soluble inether; apparently the unreacted amine or "CS2 in .the crude product .solubilizes the .thioc'arbanilide. v r

A sample cif'fres'lily 'redistilled xylidine (amixture of various isomeric xylidines) was "then tested "for color stabilityby "heating in an open testtube atl l'fla". as an. acceleratedstability' test,

' periodically determining the color, or optical density, in a"Hellige-Di1ler photoelectric colorimeter, Iusing.afNorithSkyZfilter. J21-hours were required 'for the sample to darken 'to a color density of .110, .wliihisequivalen't to'i10% transni'ission-wherejpure water, gi'v'es"100% transmiseating that f the stfibili'zefi xilidinerequired 1.40 hours to .aar'ken to the Lsarh'eexteht, .i..e. 10%

transmissioh,.as the unstabilized xylidine darken'ed. duiin'gZlI'hQwiS nffhe'ating.

' -'-EXAMPLE -2 .-A series-ofxtestswas madedn order to compare Suhdil'uentslmaybepresent in amounts ranging the relative qefiectiveness .of an :addition agent prepared as-described above according to this :invention, as distinguished vfrom .several -mater1als recently 1 marketed for ea similar use, :such amaterials being referred to herein as commercial additives A and B, respectively. In this case the additive was prepared from pure p-xylidine and carbon disulfide, thus producing a tetramethyl thiccarbanilide, di-p-xylyl thio urea, The results of this series of tests which were carried out by heating a freshly redistilled xylidine containing 0.2% of the various additives in an open test tube in an oven at 194 F., are shown in Table I.

disulfide is much slower with mixed commercial xylidines than with pure p-xylidine, although the final products do not differ greatly in potency as color stabilizers. It has also been found that the reaction occurs in steps. The first step is believed to comprise the additionofcarbon disulfide to a xylidine moleculefwhile the second step, which ordinarily is quite slow, probably comprises reaction of the intermediate product with a second molecule of xylidine, evolving hydrogen sulfide. At least, after removing unreacted carbon disulfide by distillation from the reaction mixture,

Table I No. of Hrs. Rfiqllled flor t e amp e Test to Darken to 10% Transmission Xylidine alone. Xylidine 0.2% commercial Additive A" 29 Xylidine 02% commercial Additive B.. 30 Xylidine 0.2% Additive of this inven 83 tion EXAMPLE 3 g r Another series of color stability tests at 194 F. was made employing a difierent freshly distilled commercial xylidine as the base stock. The results obtained with 0.2 of commercial additive C, and with 0.05% and 0.01% of the additive pre pared as described in Example 1 are shown in The tests of Examples 2 and 3 show that the additive prepared according to this invention is far more active than commercial additives A, B and C. I

A suitable method of purifying the additives of this invention, after reaction of the commercial aromatic amine, such as xylidine with carbon disulfide, is to extract the unreacted amine from the crude reaction product by a suitable solvent such as petroleum ether. If desired, the white solid product may be recrystallized, for example from hot alcohol, to obtain essentially pure dixylyl thiourea. During the reaction of the xylidine with carbon disulfide, the evolved hydrogen sulfide gas may either be permitted to escape or stripped out with an inert gas or may be reacted with alkali which may be added directly to the reaction mixture. The reaction is hastened by heating, but too high a temperature causes deep seated changes and should be avoided.

' Instead of using a commercial xylidine as raw material one may use other commercial aromatic amines'such as aniline, toluidine, or any one par-. ticular xylidineisomer, such as p-xylidine, or even It'has been found that' the reaction of carbon is hydrogen sulfide continues to evolve for hours even on warming. It is believed that the stepwise mechanism offers an explanation for the experimental fact that carbon disulfide itself is much less potent as a color stabilizer of amines than are the products of this invention, in that the intermediate product is a poor color stabilizer, and serious color degradation occurs before the concentration of the final product reaches an effective amount. Another important advantage over the use of carbon disulfide is the absence of hydrogen sulfide dissolved in thestabilized amine which increases corrosion of metals, and when used in motor fuels increases the copper dish gum and decreases susceptibility to octane number improvement by tetraethyl lead. On the other hand, satisfactory results can be obtained by adding carbon disulfide to the amine to be stabilized and completing the reaction prior to ex posure to the atmosphere, by blowing with an inert gas or treating with alkali, such as sodium hydroxide or carbonate, to remove hydrogen sulfide.

EXAMPLE 4 In another series of tests at 194 F. on xylidine. from a difierent source, the additive prepared as described in Example 1 was compared with com mercial additives A, B, C, D and E. The results are shown in Table III. 4

Table III No. of Hrs.

Required for the Sample Test No. to Darkcn Transmission Xylidine alone 16 Xylidine+0.24% commercial Additive A 16 Xylidine+0.24% commercial Additive B 15 Xylidine+0.24% commercial Additive 0.. 21 Xylidine+0.24% commercial Additive D. 13 Xylidine+0.24% commercial Additive E 11 Xylidme+0.24% commercial Additive C +01% Additive of this invention 27 The above examples show the superiority of' the additive of this invention over other addi tives.. Also shown is the difference in response to'various additives of the various base xylidines, and the fact that in ever case the response. to' the additive of this invention is very great.

Although the mechanism of the operation of. the invention is not understood with certainty, it is believed that during the storage, the aromatic amine must necessarily undergo some chemical reaction such asoxidation, polymerization or cone densation, which is subject to inhibition by the 'thiocarbanilide or alkylated derivative thereof;

.It is not intended that this invention be lim-,.

ited to the particular materials which have been given merely for the sake of illustration, nor by any theory as totl e mechanism of the opera-j tion of 'the invention, butio'nly by the appended claim in which it is intended to claim all novelty inherent in the invention as well as all modifications coming within the scope and spirit of the invention.

I claim:

The method of stabilizing commercial xylidine against discoloration during storage which consists in reacting carbon disulfide with a small portion thereof to form corresponding tetramethyl thiocarbanilide derivatives, recovering the latter in substantially pure crystalline form and adding the same in a concentration of about .01 to 3.0% to the large portion of xylidine to be stabilized.

JOHN C. MUNDAY.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 6 UNITED STATES PATENTS Name Date Rather et al. Jul 4, 1933 Bond Feb. 20, 1934 Missbach June 9, 1936 Jenkins Jan. 25, 1938 Martin Apr. 11, 1939 Carswell June 6, 1939 Robertson Jan. 20, 1948 FOREIGN PATENTS Country Date Great Britain Dec. 29, 1930 Great Britain July 22, 1935 OTHER REFERENCES Chem. Abstracts, vol. 28 (1934), page 1335. 

